As posted on the Canadian Foreign Affairs website, Canadians travelling to and from the Dominican Republic will require passports starting on the 30th of April, 2012. If travelling through the US, you have to make sure that your passport has a validity of 6 months after your return but for the moment no such requirement applies for direct flights.

So Canadians living in the DR or long-term visitors, make sure your passports are valid if you plan on travelling soon!